(a) Field of the Invention
The present invention relates to a method and a system for compensating for a position error of a step motor.
(b) Description of the Related Art
A step motor can be controlled at an even rotation angle through a simple control circuit even though a resolution is low, and can perform a highly precise position control even without an expensive position sensor. Due to these advantages, the step motor is widely used to computer peripherals, a video tape recorder (VTR), an X-Y table, a semiconductor device, a direction control device of a security camera, or the like.
The step motor has been generally controlled by a basic angle control method which is referred to as a full step control method or a half step control method. According to the basic angle control method, the step motor rotates by a step angle, i.e., 1.8° or 0.9° per one input pulse. Since the step motor rotates by the step angle which is a relatively great angle, a small vibration occurs at every rotation at a low speed so that the motor cannot smoothly rotate, and this small vibration at a low and a medium speed can cause a shaft vibration to increase as high as the motor cannot rotate (stall phenomenon).
In order to solve such drawbacks of the basic angle control method, a micro step control method has been introduced. The micro step control method is a method of driving the step motor in a smaller angle (micro step) than the step angle, that is, a method of controlling the step motor with an increased resolution of the rotating angle. The increased resolution of the rotating angle by the micro step control method may decrease the noise and the vibration at a low speed, and hence the stall of the motor can be prevented.
However, to increase the resolution of the rotating angle of the motor by the micro step driving is not to enhance the preciseness of the rotating angle of the motor. That is, whether the step motor actually precisely rotates by a very small angle during the micro step driving, that is, the preciseness of the rotating angle, is different from the resolution of the rotating angle of the motor.
For example, if the conventional step motor is driven by a full step with the step angle of 1.8°, the motor rotates by 1.8° per one pulse of a rotation command, and rotates by 0.9° at the half step driving. On the other hand, according to the micro step driving, the motor rotates by 360/25000(=0.0144)° per one rotation command so as to enhance the resolution. However, the step motor intrinsically has the possibility of a position error, and generally has a position error of about ±5% even in case of the micro step driving. In case that a particularly precise position control is required, the position error of ±5% is not negligible.